BACILLUS TYPHOSUS. 



421 



power dry lens (about 1/8 inch) being used, or, some- 

 what less serviceably, a 1/12 oil-immersion lens. 



THE REACTION. If the reaction takes place rapidly 

 the first glance through the microscope reveals the com- 

 pleted reaction, all the bacilli being in loose clumps 

 and nearly or altogether motionless (Fig. 53). Be- 



FlG. 53. 



Widal reaction. Bacilli gathered into one large and two small clumps, the 

 few isolated bacteria being motionless or almost so. 



tween the clumps are clear spaces containing few or no 

 isolated bacilli. If the reaction is a little less complete 

 a few bacilli may be found moving slowly between the 

 clumps in an aimless way, while others attached to the 

 clumps by one end are apparently trying to pull away, 

 much as a fly caught on fly-paper struggles for freedom. 

 If the agglutinating substances are still less abundant 

 the reaction may be watched through the whole course 

 of its development. Immediately after mixing the blood 

 and culture together it will be noticed that the bacilli 



